Within the radio astronomic community there is a growing interest on very wide band receiver systems capable of operating with high levels of sensitivity and at the very low noise characteristics of modern radio astronomic instruments. These new instruments will allow observation of astronomical sources from the boundary between the dark universe and that of the first galaxy formation to study very fast astronomical phenomena. In order to do this, these new classifications of instruments require an ideally instantaneous bandwidth from 100 MHz and 25 GHz. For example, this is the aim of the international collaboration known as the Square Kilometer Array (SKA). Therefore the need for ultra-wide band radio telescope systems is very pressing.
Currently there are receiver systems with noise temperatures of a few degrees Kelvin operating over a decade of bandwidth. In addition, radio telescope arrays such as the Allen Telescope Array (ATA) currently being completed at Berkeley operates with such low noise receiver systems in conjunction with an off-axis Gregorian reflector optics and an ultra wide feed that operates from 0.5 to 12 GHz. While the ATA feed has good input matching over a very wide frequency band, nevertheless, it also has two main drawbacks. One drawback is its relatively large aspect ratio, i.e., the ratio of its width dimension to its height dimension, and the second is the location of the phase center of the feed varies as a function of frequency. Accordingly, current receiver systems cannot take full advantage of their large bandwidth with the highest sensitivity for simultaneous observations using the full bandwidth, or in the alternative has to be limited to a narrower bandwidth with the aid of a motorized re-focusing mechanism.
One alternative wideband feed is the Chalmers Feed which is a low profile feed and also has a frequency invariant phase center location. However, a major disadvantage of the Chalmers Feed is somewhat poor input matching (currently, at some frequencies within the frequency band only better than −7 dB) that reduces its effective frequency band coverage.
Based on the foregoing it can be seen that a need exists for an ultra-wide band antenna which has a phase center which is invariant to frequency, which is compact and has a low profile, and which has an input matching better than what is currently known.